对称二叉树 · 交互式算法学习

这是一组同题正确实现，独立于上方当前动画方法；不同语言可能采用另一种正确策略。

1/**2 * Definition for a binary tree node.3 * public class TreeNode {4 *     int val;5 *     TreeNode left;6 *     TreeNode right;7 *     TreeNode() {}8 *     TreeNode(int val) { this.val = val; }9 *     TreeNode(int val, TreeNode left, TreeNode right) {10 *         this.val = val;11 *         this.left = left;12 *         this.right = right;13 *     }14 * }15 */16class Solution {17    public boolean isSymmetric(TreeNode root) {18        return dfs(root.left, root.right);19    }20 21    private boolean dfs(TreeNode root1, TreeNode root2) {22        if (root1 == root2) {23            return true;24        }25        if (root1 == null || root2 == null || root1.val != root2.val) {26            return false;27        }28        return dfs(root1.left, root2.right) && dfs(root1.right, root2.left);29    }30}